The NH2-terminal blocking group of the Ca2+-binding B-subunit of calcineurin (protein phosphatase-2B) has been identified as myristic acid by fast atom bombardment mass spectrometry and gas chromatography. The sequence, myristyl-Gly-Asn-Glu-Ala-, is very similar to that of the catalytic subunit of cyclic AMP-dependent protein kinase, the only other protein known to contain this fatty acid. This finding, and the elution of all myristyl peptides at 57% acetonitrile on reverse phase HPLC, may facilitate the identification of other proteins with this blocking group.